The biggest problem with such a gamemode in multiplayer is that all players need to be present to the action when it slows down / speeds up otherwise it will be kinda stupid being on the other side of the map, having nothing to do with it and then suddenly slowmo.
The best use this could possibly have is when critical events happen (I.E. Capture Point captured, game started, game ended).
Alternatively, for single player campaigns, but still not that much of a use there. Except for SuperHot.